1. Field of the Invention
This invention relates to an electrophotographic photosensitive member, and more particularly, to an electrophotographic photosensitive member having an improved electroconductive layer.
2. Description of the Prior Art
An electrophotographic photosensitive member is fundamentally composed of a substrate and a photosensitive member. However, where the substrate is an insulating material such as paper, plastics and the like, an electroconductive film should be provided on the substrate so as to flow electric charges.
Where the substrate is made of a metal such as aluminum, copper, brass, stainless steel and the like, an electroconductive film is not necessary, but it is advantageous to form a coating layer on the substrate since this coating layer can improve the coating characteristics of the photosensitive layer, protect the photosensitive layer against electric breakdown, and cover defects on the surface of the substrate. Since the coating layer should have an electrostatically sufficiently low resistance, the coating layer should be an electroconductive film.
The electroconductive film as mentioned above is usually called an electroconductive layer. This electroconductive layer is conventionally composed of an electrolyte such as lithium chloride, sodium chloride and the like dissolved in a water-soluble resin such as polyvinyl alcohol, methylcellulose and the like, or a high polymer electrolyte such as high polymer quaternary ammonium salt, high polymer sulfonates, and the like. However, resistance of such electroconductive layer increases under low humidity conditions so that it is not suitable for electrophotographic photosensitive members. In addition, when an electroconductive layer is formed for the purpose of covering defects on the surface of a substrate, it is necessary to have a thick electroconductive layer and therefore, it is necessary to lower the resistance of the electroconductive layer.
An electroconductive layer is difficult to be produced by using only a single resin. In general, electroconductive powders are dispersed in a resin to produce an electroconductive layer.
As the electroconductive powders, there are used metal powders such as nickel, copper, silver, aluminum and the like, metal oxide powders such as iron oxide, tin oxide, antimony oxide, indium oxide and the like, carbon powders and the like. When these electroconductive powders are dispersed in resins, the resulting electroconductive coating material is composed of a dispersion of powders, and therefore, the surface of the resulting electroconductive layer is inevitably irregular or rough.
The surface property of the electroconductive layer largely contributes to the image quality obtained by the electrophotographic photosensitive member so that the surface of the electroconductive layer is required to be very clear and smooth.
However, as mentioned above, conventional electroconductive layers have defective surface property and therefore, electrophotographic photosensitive member using such electroconductive layer can not give good image quality.